The research in this proposal is a molecular biological approach to understand the mechanisms of gene expression in the early region of polyoma virus. Efforts revolve around hr-t mutants of polyoma virus, which map in the proximal early region of the viral genome and define a function essential for both virus growth and malignant transformation of cells. Deletion and point hr-t mutants will be analyzed at three levels: 1) DNA sequencing to define the alterations in the viral DNAs, 2) determination of patterns of transcription and RNA splicing of wild type and mutant viral mRNAs, and 3) in vitro translation of viral mRNAs. It is hoped that these experiments will shed some light on the complexities of gene expression operating in this region of the viral genome and possibly also on the questions of the signals or sequences in RNA transcripts essential for proper splicing. Efforts will also be made to isolate temperature-sensitive mutants in the hr-t gene.